The Ugi reaction with 2-substituted cyclic imines. Synthesis of substituted proline and homoproline derivatives

The Ugi three-component reaction with 2-substituted five-, six-, and seven-membered cyclic imines was investigated. The reaction opens a new route to substituted proline and homoproline derivatives. It was shown that the method is efficient for the one-step preparation of seminatural dipeptides containing natural amino acid residues, and fragments of substituted proline or pipecolinic acid. The scope and limitation of the approach are discussed.